Polishing pad, method for manufacturing polishing pad, and polishing method applying polishing pad

ABSTRACT

A polishing pad includes a polyurethane, wherein the polyurethane includes in its main chain a silane repeating unit represented by Formula 1, wherein the number of defects on a substrate after polishing with the polishing pad and a fumed silica slurry is about 40 or less 
     
       
         
         
             
             
         
       
     
     wherein R 11  and R 12  are each independently hydrogen or C 1 -C 10  alkyl groups, and n is an integer from 1 to 30.

BACKGROUND 1. Field

The present disclosure relates to a polishing pad, a method for manufacturing a polishing pad, and a polishing method using a polishing pad.

2. Description of the Background

Polishing pads are used in chemical mechanical planarization (CMP) for industrially easy surface micromachining and can be widely used to planarize silicon wafers, memory disks, and magnetic disks for semiconductor devices, optical materials such as optical lenses and reflective mirrors, and other materials such as glass plates and metals where high surface planarity is required.

Along with the integration and miniaturization of semiconductor circuits, the importance of CMP process is more and more emphasized. CMP pads are essential elements in CMP process for semiconductor fabrication and play an important role in the determination of CMP performance.

CMP pads are required to have various performances. Particularly, the number of defects in materials greatly affects the yield of the materials and can thus be considered as a crucial factor in determining the quality of CMP pads.

The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the disclosure.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one general aspect, a polishing pad includes a polyurethane including in its main chain a silane repeating unit represented by Formula 1, wherein the number of defects on a substrate after polishing with the polishing pad and a fumed silica slurry is 40 or less,

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to 30.

The polyurethane may include in its main chain a repeating unit represented by Formula 2-1 or 2-2:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and R₂₁ is —Si(R₁₃)(R₁₄)(R₂₂)—, wherein R₁₃ and R₁₄ are each independently hydrogen or a C₁-C₁₀ alkyl group, and R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), and n is an integer from 1 to 30.

The difference of a contact angle of the polishing pad for pure water and a contact angle of the polishing pad for a fumed silica slurry may be 1.5 to 5, as calculated by Equation 1:

Ad _((p−f))(%)=[100×(Ap−Af)]/Ap   [Equation 1]

where Ap is the contact angle for pure water, Af is the contact angle for a fumed silica slurry, and Ad_((p−f)) is the difference between the contact angles.

The polyurethane may be in the form of a foamed body with an average pore size of 10to 30μm.

The polyurethane may have a Shore D hardness of 55 to 65.

The polishing pad may further include a top pad including the polyurethane and a sub-pad disposed on the top pad.

The sub-pad may be a non-woven fabric or suede type material.

In another general aspect, a polishing pad includes a top pad as a polyurethane polishing layer, wherein the polyurethane polishing layer includes a foamed body of a urethane composition, wherein the urethane composition includes a urethane prepolymer, a curing agent, and a foaming agent, wherein the urethane prepolymer is a copolymer of a prepolymer composition including an isocyanate compound, an alcohol compound, and a silane compound, wherein the silane compound includes a silane repeating unit and has at least one end terminated with a hydroxyl, amine or epoxy group, and the silane repeating unit is represented by Formula 1:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to 30.

The prepolymer composition may include the silane compound in an amount of 0.1 to 5% by weight, based on the total weight of the prepolymer composition.

The top pad may reduce a number of defects on a silicon wafer after polishing by 80% or more compared to polyurethane foamed body without the silane repeating unit represented by Formula 1.

The silane compound may be represented by Formula 3:

wherein R₁₁, R₁₂, R₁₃, and R₁₄ are each independently hydrogen or C₁-C₁₀ alkyl groups, R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), R₃₁ is C₁-C₂₀ alkylene groups, R₄₁ and R₄₂ are each independently a hydroxyl, amine or epoxy group, and n is an integer from 1 to 30.

The % NCO of the prepolymer may be from 8 to 12% by weight.

In another general aspect, a method for manufacturing a polishing pad includes i) preparing a polyurethane in the form of a foamed body with polymerizing a urethane composition, ii) manufacturing a top pad comprising the polyurethane, and iii) fixing the top pad to a sub-pad by lamination, wherein the urethane composition comprises a urethane prepolymer, a curing agent, and a foaming agent, and wherein the foamed body comprises a repeating unit represented by Formula 1, and the main chain of the polyurethane contains the silane repeating unit:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to 30.

The urethane prepolymer may be prepared by a method including allowing a prepolymer composition to react at 50 to 120° C., and the % NCO of the urethane prepolymer is from 8 to 12% by weight, wherein the prepolymer composition may include an isocyanate compound, an alcohol compound, and a silane, wherein the silane compound may include the silane repeating unit of Formula 1 and at least one end group with a hydroxyl, amine or epoxy group.

The preparation of the urethane prepolymer may include mixing the isocyanate compound and the alcohol compound to prepare a first composition and allowing the first composition to react at 60 to 100° C. for 1 to 5 hours to prepare a first polymer (first step), and mixing the first polymer and the silane compound to prepare a second composition and allowing the second composition to react at 60 to 100° C. for 0.5 to 3 hours to prepare a second polymer (second step).

A method for producing a polished wafer may include mounting the polishing pad and an unpolished wafer in a chemical mechanical planarization (CMP) polisher and polishing the unpolished wafer with the polishing pad while feeding a polishing slurry into the CMP polisher.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual cross-sectional view of a polishing pad including a top pad according to one or more examples.

FIG. 2 shows electron microscopy images of pores of top pads manufactured in (a) Example 1, (b) Example 2, and (c) Comparative Example 1.

FIG. 3 is a graph comparing the Removal Rate (RR, above) and the cutting rate (below) of the polishing pad prepared in Examples 1 and 2 (ex. 1 and ex. 2) with Comparative Example 1 (c.ex. 1).

FIG. 4 is a graph comparing the results of measuring the number of defects (#defect per about 300 mm diameter disc) of silicon wafer polished using the polishing pad prepared in Examples 1 and 2 (ex. 1 and ex. 2) with Comparative Example 1 (c.ex. 1).

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent after an understanding of this disclosure. For example, the sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent after an understanding of this disclosure, with the exception of operations necessarily occurring in a certain order. Also, descriptions of features that are known in the art may be omitted for increased clarity and conciseness.

The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided merely to illustrate some of the many possible ways of implementing the methods, apparatuses, and/or systems described herein that will be apparent after an understanding of this disclosure. Hereinafter, while embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, it is noted that examples are not limited to the same.

As used herein, the terms “about”, “substantially”, etc. are intended to allow some leeway in mathematical exactness to account for tolerances that are acceptable in the trade and to prevent any unconscientious violator from unduly taking advantage of the disclosure in which exact or absolute numerical values are given so as to help understand the application. Due to manufacturing techniques and/or tolerances, variations of the shapes shown in the drawings may occur. Thus, the examples described herein are not limited to the specific shapes shown in the drawings, but include changes in shape that occur during manufacturing.

In the present specification, the term “combination of” included in Markush type description means mixture or combination of one or more elements described in Markush type and thereby means that the disclosure includes one or more elements selected from the Markush group.

As used herein, the term “and/or” includes any one and any combination of any two or more of the associated listed items; likewise, “at least one of” includes any one and any combination of any two or more of the associated listed items.

Although terms such as “first,” “second,” and “third” may be used herein to describe various members, components, regions, layers, or sections, these members, components, regions, layers, or sections are not to be limited by these terms. Rather, these terms are only used to distinguish one member, component, region, layer, or section from another member, component, region, layer, or section. Thus, a first member, component, region, layer, or section referred to in examples described herein may also be referred to as a second member, component, region, layer, or section without departing from the teachings of the examples.

Spatially relative terms such as “above,” “upper,” “below,” and “lower” may be used herein for ease of description to describe one element's relationship to another element as shown in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, an element described as being “above” or “upper” relative to another element will then be “below” or “lower” relative to the other element. Thus, the term “above” encompasses both the above and below orientations depending on the spatial orientation of the device. The device may also be oriented in other ways (for example, rotated 90 degrees or at other orientations), and the spatially relative terms used herein are to be interpreted accordingly.

Throughout the specification, when an element, such as a layer, region, or substrate, is described as being “on,” “connected to,” or “coupled to” another element, it may be directly “on,” “connected to,” or “coupled to” the other element, or there may be one or more other elements intervening therebetween. In contrast, when an element is described as being “directly on,” “directly connected to,” or “directly coupled to” another element, there can be no other elements intervening therebetween.

The terminology used herein is for describing various examples only, and is not to be used to limit the disclosure. The articles “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “includes,” and “has” specify the presence of stated features, numbers, operations, members, elements, and/or combinations thereof, but do not preclude the presence or addition of one or more other features, numbers, operations, members, elements, and/or combinations thereof.

The features of the examples described herein may be combined in various ways as will be apparent after an understanding of this disclosure. Further, although the examples described herein have a variety of configurations, other configurations are possible as will be apparent after an understanding of this disclosure.

Herein, it is noted that use of the term “may” with respect to an example, for example, as to what an example may include or implement, means that at least one example exists in which such a feature is included or implemented while all examples are not limited thereto.

One or more examples described herein disclose a polishing pad for producing a polished substrate with a reduced number of defects, a method for manufacturing the polishing pad, and a polishing method using the polishing pad.

Polishing pads for chemical mechanical planarization according to the one or more examples disclosed herein, rapidly and accurately polish substrates without defects such as scratches or chatter marks on the substrate surfaces. Example polishing pads for producing polished substrates that can reduce the number of defects while maintaining their other properties at levels equal to those of conventional polishing pads are described herein. As described in the one or more examples, use of a polishing pad with a high contact angle for a slurry solution can lead to a significant reduction in the number of defects on a wafer after polishing while preventing the slurry particles from sticking to the polishing pad.

FIG. 1 is a conceptual cross-sectional view of a polishing pad according to one or more examples. The examples will be described in more detail with reference to FIG. 1. The polishing pad 100 comprises a polyurethane with a silane repeating unit represented by Formula 1:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to 30 in Formula 1.

For example, in Formula 1, R₁₁ and R₁₂ may each be independently hydrogen or C₁-C₅ alkyl groups, and n may be an integer from 8 to 28.

The silane repeating unit represented by Formula 1 is included in the main chain of the polyurethane. This structure may allow the polishing pad 100 to stably and relatively uniformly polish a substrate with a reduced number of defects by chemical mechanical planarization. For example, the use of the polishing pad in combination with a fumed silica slurry is very effective in suppressing the formation of defects on a substrate after polishing.

For example, the polyurethane may comprise a repeating unit represented by Formula 2-1 or 2-2:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and R₂₁ is —Si(R₁₃)(R₁₄)(R₂₂)—, wherein R₁₃ and R₁₄ are each independently hydrogen or a C₁-C₁₀ alkyl group, and R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), and n is an integer from 1 to 30.

For example, in Formula 2-1 or 2-2, R₁₁ and R₁₂ are each independently hydrogen or C₁-C₅ alkyl groups, and R₂₁ is —Si(R₁₃)(R₁₄)(R₂₂)—, wherein R₁₃ and R₁₄ are each independently hydrogen or a C₁-C₅ alkyl group, and R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 2 to 12), and n is an integer from 8 to 28.

The polishing pad 100 may comprise 0.1 to 5% by weight of the silane repeating unit represented by Formula 2-1 or 2-2. In this case, occurrence of the stickiness of slurry particles on the surface or pores of the polishing pad can be efficiently prevented, as intended in the example.

For example, the Formula 2-1 or 2-2 may be following Formula 2-3 or 2-4, respectively:

wherein n is an integer from 8 to 28, p is an integer from 1 to 10.

For example, in Formula 2-3 or 2-4, n may be an integer from 10 to 25, p may be an integer from 1 to 5.

Due to these features, the polyurethane can be used to constitute the polishing pad 100. The polishing pad may comprise a top pad 10 and a sub-pad 30, and the polyurethane may be applied to the top pad 10 of the polishing pad.

The polyurethane may be in the form of a foamed body.

The polyurethane in the form of a foamed body may be prepared by mixing a polyurethane composition with a foaming agent. The foaming agent may be selected from the group consisting of gaseous foaming agents, solid foaming agents, liquid foaming agents, and combinations thereof.

When the polishing pad 100 comprising a top pad 10 is used in combination with a fumed silica slurry to polish a silicon oxide film, a number of defects on surface of wafer after polishing may be reduced. The number of defects may be for example, 40 or less, 25 or less or 10 or less. The wafer may be disc-shaped one with diameter about 300 mm or more. The wafer may have surface area of about 70685.83 mm² or more. A number of defects on surface of wafer may be detected based on the surface area.

The number of defects is detected using a defect inspection system (XP+, Tencor) after the silicon wafer is polished using a CMP polisher, washed, and dried.

The polishing is performed by the following standard procedure. First, a 300 mm-silicon wafer deposited with silicon oxide is mounted in a CMP polisher such that the silicon oxide layer of the silicon wafer is in contact with the surface of a platen attached with the polishing pad 100. Then, the silicon wafer is polished at a polishing load of 4.0 psi while rotating at 150 rpm for 60 seconds. For this polishing, a slurry such as a fumed silica or ceria slurry may be used.

The fumed silica slurry may have a pH of 10.5 specifically and may comprise silica with an average particle size of 150 nm dispersed therein.

For example, the fumed silica slurry may be prepared by the following procedure.

First, a base solution at pH 10.5 comprising a first pH adjusting agent and ultrapure water is prepared. Ammonia, potassium hydroxide or sodium hydroxide may be used as the first pH adjusting agent. Then, 12% by weight of fumed silica (OCI) is added portion wise to the base solution. The resulting mixture is dispersed using an ultrasonicator at 9000 rpm for about 4 hours to prepare a silica base solution. The silica base solution is further dispersed using a high-pressure homogenizer, added with 0.5 to 2% by weight of an ammonium additive, and stirred for additional 1 hour. Thereafter, 0.01 to 0.1% by weight of a nonionic surfactant (for example, polyethylene glycol) and a second pH adjusting agent are added to prepare a mixed slurry solution at pH 10.5. Ammonia, potassium hydroxide, sodium hydroxide, nitric acid or sulfonic acid may be used as the second pH adjusting agent. The mixed slurry solution is passed through slurry filters with 3.5 μm and 1 μm pore sizes (Micropore) to prepare the final fumed silica slurry. The final fumed silica slurry may have a pH of 10.5 and comprise fumed silica with an average particle size of 150 nm dispersed therein. The average particle size of the fumed silica is measured with a Zetasizer (nano-ZS 90, Malvern). The slurry is used as a reference solution for subsequent contact angle measurement.

When a silicon wafer is polished with the polishing pad 100 at a cutting rate of 45 to 55 μm/hr, 40 or less, 25 or less or 10 or less, defects may occur on the silicon wafer.

When a silicon wafer is polished with the polishing pad 100 at a removal rate of 2600 to 2900 Å/min, 40 or less, 25 or less or 10 or less defects may occur on the silicon wafer.

The difference between contact angles of the polishing pad 100 for pure water and the fumed silica slurry may be 1.5 to 5 or 2 to 4, as calculated by Equation 1:

Ad _((p−f))(%)=[100×(Ap−Af)]/Ap   [Equation 1]

where Ap is the contact angle for pure water, Af is the contact angle for the fumed silica slurry, and Ad_((p−f)) is the difference between the contact angles.

When the difference between the contact angles is within the range defined above, the use of the polishing pad in combination with the fumed silica slurry may lead to a significant reduction in the number of defects while maintaining its removal rate and cutting rate at levels substantially equal to or better than those of conventional polishing pads.

The contact angles are measured at room temperature. The fumed silica slurry having a pH of 10.5 and containing fumed silica 12% by weight with an average particle size of 150 nm dispersed therein is used as a reference for the contact angle measurement. The composition and preparation method of the fumed silica slurry are the same as those described above and a further detailed description thereof is thus omitted.

The contact angle of the polishing pad 100 for the fumed silica slurry may be from 85 to 120°.

The contact angle of the polishing pad 100 for pure water may be from 85 to 125°.

The contact angle of the polishing pad 100 for pure water may be different by at leas 1.5°, for example, at least 1.8° or at least 2°, from that for the fumed silica slurry.

The contact angle of the polishing pad 100 for pure water may be different by 1.2 to 5° or 1.5 to 4° from that for the fumed silica slurry.

Since the contact angle of the polishing pad 100 for pure water is relatively largely different from that for the fumed silica slurry, as mentioned above, the repulsive force between the surface of the polishing pad and the slurry particles may increase when the polishing pad is in contact with the polishing slurry. And as a result, occurrence of stickiness of the slurry particles on the surface or pores of the polishing pad can be considerably reduced, and this may allow ensuring high polishing quality.

When the polishing pad 100 whose contact angle for the slurry is relatively largely different from that for pure water is a foamed pad, the number of defects can be more significantly reduced. In many cases, slurry particles may enter and stick to surface micropores of foamed polishing pads. It is considered that the stuck slurry particles may form defects on the surface of substrates after polishing. The polishing pad of the examples may significantly reduce this phenomenon.

In the examples, the presence of the silane repeating unit in the main chain of the polyurethane constituting the polishing pad 100 particularly may induce a substantially large repulsive force between the silica particles and the polyurethane surface so that the number of defects can be significantly reduced while substantially maintaining other properties (for example, removal rate and cutting rate) of the polishing pad used in combination with a slurry at levels equal to those of conventional polishing pads.

The polishing pad 100 may comprise a top pad 10, a first adhesive layer 15 disposed on one surface of the top pad, and a sub-pad 30 disposed on one surface of the first adhesive layer 15 opposite the top pad 10.

The top pad 10 may be composed of the polyurethane in the form of a foamed body whose features have been described above. The top pad 10 may have an average pore size of 10 to 30μm, which is preferable in improving the polishing efficiency of the polishing pad.

The polyurethane in the form of a foamed body may have an area proportion of 36 to 44%. 350 to 500 pores may be present per unit area (about 0.3 cm²) of the polyurethane in the form of a foamed body. Due to these features, the use of the polyurethane top pad 10 in the form of a foamed body enables efficient wafer polishing.

The top pad 10 may have a Shore D hardness in the range of 55 to 65. Within this range, high polishing efficiency may be achieved.

The top pad 10 may have a thickness in the range of 1.5 to 3 mm. Within this range, high polishing efficiency may be achieved.

The sub-pad 30 may have an Asker C hardness of 60 to 90.

The sub-pad 30 may be a non-woven fabric or suede type.

The sub-pad 30 may have a thickness of 0.5 to 1 mm.

The top pad 10 may be attached to the sub-pad 30 through the first adhesive layer 15. In an example, the first adhesive layer 15 may be a hot-melt adhesive layer.

A rubber adhesive may be applied to the other surface of the sub-pad 30 opposite the first adhesive layer 15 to form a second adhesive layer 35.

A film 50 may be disposed on the other surface of the second adhesive layer 35 disposed on the other surface of the sub-pad 30. The film may be, for example, a PET film. A rubber adhesive layer may be formed as a third adhesive layer 55 on the film 50.

The other surface of the sub-pad 30 may be fixed to a platen of a polisher through the rubber adhesive layer 35.

A polishing pad 100 according to one or more further examples may comprise a top pad 10 as a polyurethane polishing layer. The polyurethane polishing layer may comprise a foamed body which may be a polymerized one of a urethane composition comprising a urethane prepolymer, a curing agent, and a foaming agent. The urethane prepolymer may be a copolymer of a prepolymer composition comprising an isocyanate compound, an alcohol compound, and a silane compound comprising a silane repeating unit as described below.

The silane compound may be a compound that can react with the isocyanate such as silane modified polyol and silane modified amine to introduce the silane repeating unit into the main chain of the urethane.

For example, the silane compound may comprise the silane repeating unit of Formula 1, and may be terminated with a hydroxyl, amine or epoxy group at at least one end.

In the Formula 1, R₁₁, R₁₂, and n are the same as that described above and a further detailed description thereof is thus omitted.

The prepolymer composition may comprise the silane compound in an amount of 0.1 to 5% by weight. For example, the prepolymer composition may comprise the silane compound in an amount of 1 to 3% by weight or 1.5 to 2.5% by weight, based on the total weight of the prepolymer composition.

If the silane compound is present in an amount less than 0.1% by weight, based on the total weight of the prepolymer composition, the effect of the silane compound to reduce the number of defects may be inadequate. Meanwhile, if the silane compound is present in an amount exceeding 5% by weight, gelation may occur during synthesis, making it difficult to achieve the desired physical properties. The presence of the silane compound in an amount of 0.1 to 5% by weight enables the polyurethane polishing pad to effectively reduce the number of defects.

For example, the top pad 10 may reduce the number of defects of a silicon wafer after polishing by 80% or more, 85% or more, or 90% or more compared to polyurethane foamed body without the silane repeating unit represented by Formula 1. The reduced number of defects may be obtained when the cutting rate and removal rate are substantially equal to or greater than those of conventional polyurethane polishing pads, contributing to a significant reduction in the defective proportion of silicon wafers.

The silane compound may be represented by Formula 3:

wherein R₁₁, R₁₂, R₁₃, and R₁₄ are each independently hydrogen or C₁-C₁₀ alkyl groups, R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), R₃₁ is C₁-C₂₀ alkylene groups, R₄₁ and R₄₂ are each independently a hydroxyl, amine or epoxy group, and n is an integer from 1 to 30.

For example, in Formula 3, R₁₁, R₁₂, R₁₃, and R₁₄ may each be independently hydrogen or C₁-C₅ alkyl groups, R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 2 to 12), R₃₁ may be C₁-C₁₀ alkylene groups, R₄₁ and R₄₂ may each be independently a hydroxyl, amine or epoxy group, and n may be an integer from 8 to 28.

For example, in Formula 3, R₁₁, R₁₂, R₁₃, and R₁₄ may each be independently hydrogen, methyl, or ethyl, R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 2 to 12), R₃1 may be C₁-C₅ alkylene groups, R₄₁ and R₄₂ may each be independently a hydroxyl, amine or epoxy group, and n may be an integer from 10 to 25.

The isocyanate compound may be selected from the group consisting of, but not limited to, p-phenylene diisocyanate, 1,6-hexamethylene diisocyanate, toluene diisocyanate, 1,5-naphthalene diisocyanate, isophorone diisocyanate, 4,4-diphenylmethane diisocyanate, cyclohexyl methane diisocyanate, and combinations thereof.

The alcohol compound may comprise a polyol compound, a monomeric alcohol compound or a mixture thereof.

The polyol compound may be selected from the group consisting of, but not limited to, polyester polyol, polyether polyol, polycarbonate polyol, polycaprolactone polyol, and combinations thereof.

The monomeric alcohol compound may be selected from the group consisting of, but not limited to, ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, methylpropanediol, and combinations thereof.

The urethane prepolymer may be a copolymer of the isocyanate compound, the alcohol compound, and the silane compound.

The prepolymer composition may comprise 0.7 to 1.3 parts per weight of the alcohol compound and may comprise 0.05 to 7 parts per weight of the silane compound based on 1 part per weight of the isocyanate compound.

For example, the prepolymer composition may comprise 0.8 to 1.2 parts per weight of the alcohol compound and may comprise 0.01 to 5 parts per weight of the silane compound based on 1 part per weight of the isocyanate compound.

For example, the prepolymer composition may comprise 0.85 to 1.15 parts per weight of the alcohol compound and may comprise 1.6 to 2.5 parts per weight of the silane compound based on 1 part per weight of the isocyanate compound.

When the amounts of the components are within the respective ranges defined above, the prepolymer composition can provide a polyurethane having more suitable physical properties for the polishing pad.

The % NCO of the prepolymer may be in the range of 8 to 12% by weight. Within this range, the polyurethane pad can be manufactured in the form of a foamed body with appropriate hardness and porosity more easily.

The curing agent may be, for example, an amine curing agent.

For example, the amine curing agent may be selected from the group consisting of 4,4′-methylenebis(2-chloroaniline), m-phenylenediamine, diethyltoluenediamine, hexamethylenediamine, and combinations thereof.

The foaming agent may be a gaseous foaming agent, a solid foaming agent, a liquid foaming agent or a combination thereof.

For example, the gaseous foaming agent may be an inert gas, for example, nitrogen gas or carbon dioxide gas.

The solid foaming agent may be in the form of organic hollow spheres and/or inorganic hollow spheres, for example, microspheres in which a hydrocarbon gas is encapsulated with a polymer.

Suitable liquid foaming agents may be, but are not limited to, Galden solution (triperfluoropropylamine), liquid carbon dioxide, and liquid hydrofluorocarbons.

The urethane composition may further comprise a surfactant. The surfactant may be a nonionic or ionic surfactant. The surfactant may be a silicone surfactant, for example, a copolymer containing at least one block including polydimethylsiloxane and at least one block including a polyether, polyester, polyamide or polycarbonate segment, but is not limited thereto.

The urethane composition may comprise 10 to 60 parts per weight of the curing agent, 0.1 to 10 parts per weight of the foaming agent, and 0.1 to 2 parts per weight of the surfactant based on 100 parts per weight of the urethane prepolymer. The gaseous foaming agent may be released at a rate of 0.1 to 2.0 L/min. When the amounts of the components are within the respective ranges defined above, the urethane composition may provide a polyurethane in the form of a foamed body having suitable physical properties for the polishing pad.

A method for preparing a urethane prepolymer for a polishing pad according to one or more other examples comprises allowing a prepolymer composition to react at 50 to 120° C. wherein the % NCO of the urethane prepolymer is from 8 to 12% by weight. The prepolymer composition comprises an isocyanate compound, an alcohol compound, and a silane compound including the silane repeating unit of Formula 1 and terminated with a hydroxyl, amine or epoxy group at at least one end thereof.

The preparation of the prepolymer may comprise: mixing the isocyanate compound and the alcohol compound to prepare a first composition and allowing the first composition to react at 60 to 100° C. for 1 to 5 hours to prepare a first polymer (first step); and mixing the first polymer and the silane compound to prepare a second composition and allowing the second composition to react at 60 to 100° C. for 0.5 to 3 hours to prepare a second polymer (second step).

The isocyanate compound, the alcohol compound, the silane compound, and the prepolymer composition are the same as those described above and a further detailed description thereof is thus omitted.

A method for manufacturing a polishing pad 100 according to one or more other examples comprises i) mixing a urethane prepolymer, a curing agent, and a foaming agent to prepare a urethane composition, followed by polymerization into a polyurethane in the form of a foamed body including the silane repeating unit represented by Formula 1, ii) manufacturing a top pad comprising the polyurethane, and iii) fixing the top pad to a sub-pad by lamination wherein the silane repeating unit represented by Formula 1 is present in the main chain of the polyurethane.

The isocyanate compound, the alcohol compound, the silane compound, the prepolymer composition, and the urethane composition are the same as those described above and a further detailed description thereof is thus omitted.

A method for producing a polished wafer according to still other examples comprises mounting the polishing pad 100 and an unpolished wafer in a CMP polisher and polishing the unpolished wafer with the polishing pad while feeding a polishing slurry into the CMP polisher.

For example, the unpolished wafer may be a silicon wafer, for example, a silicon wafer deposited with silicon oxide.

The polishing slurry may comprise fumed silica, colloidal silica or ceria.

The polishing may be performed by pressing the unpolished wafer against the polishing pad such that the unpolished wafer and the polishing pad are brought into contact with each other. The pressing pressure may be from 1 to 7 psi.

The polishing may be performed by rotating the unpolished wafer and/or the polishing pad. The rotational speed may be from 10 to 400 rpm.

The polishing may be performed for 1 to 10 minutes. The polishing time may be increased or decreased as needed.

The method may further include washing the polished wafer.

After separation from the CMP polisher, the polished wafer may be washed with deionized water and an inert gas (e.g., nitrogen gas).

The use of the polishing pad in the method of the present examples enables the production of a polished wafer with a reduced number of defects while possessing high levels of removal rate and cutting rate.

Hereinafter, one or more examples will be described in further detail.

1. Manufacture of Polishing Pads

EXAMPLE 1 Manufacture of Sheet-Like Top Pad

Toluene diisocyanate (TDI) as an isocyanate compound was allowed to react with polytetramethylene ether glycol (PTMEG) and diethylene glycol as polyol compounds in a 4-neck flask at 80° C. for 3 h to obtain a primary reaction product. The primary reaction product was allowed to react with silane modified polyol (Wacker® IM11, Mw:1000) in a 4-neck flask at 80° C. for 2 h to prepare a prepolymer whose % NCO was 8-12 wt %. The silane modified polyol was used in an amount of 2 wt %, based on the total weight of the prepolymer.

The prepolymer, bis(4-amino-3-chlorophenyl)methane (Ishihara) as a curing agent, and an inert gas were introduced into a casting machine equipped with a prepolymer tank, a curing agent tank, and an inert gas supply line. The prepolymer was filled in the prepolymer tank and the curing agent was filled in the curing agent tank. Nitrogen gas (N₂) was used as the inert gas. A solid foaming agent (Akzonobel) and a silicone surfactant (Evonik) were introduced into the casting machine through separate lines or were previously mixed with the prepolymer.

The equivalent ratio of the prepolymer to the curing agent in the casting machine was adjusted to 1:1. The raw materials were cast at a rate of 10 kg/min from the casting machine. The inert nitrogen (N₂) gas was fed at the rate indicated in Table 1 relative to the total flow volume.

After the raw materials were fed at high rates and mixed in a mixing head, a controlled amount of the inert gas was introduced into a mold having dimensions of 1000 mm (w)×1000 mm (l)×3 mm (h). A porous sheet-like top pad 10 having a specific gravity of 0.8-0.9 g/cc was obtained.

EXAMPLE 2 Manufacture of Sheet-Like Top Pad

Toluene diisocyanate (TDI) as an isocyanate compound was allowed to react with polytetramethylene ether glycol (PTMEG) and diethylene glycol as polyol compounds in a 4-neck flask at 80° C. for 3 h to obtain a primary reaction product. The primary reaction product was allowed to react with silane modified polyol (Wacker® IM22, Mw:2000) in a 4-neck flask at 80° C. for 2 h to prepare a prepolymer whose % NCO was 8-12 wt %. The silane modified polyol was used in an amount of 2 wt %, based on the total weight of the prepolymer.

The subsequent procedure was carried out in the same manner as in Example 1 to manufacture a sheet-like top pad 10.

COMPARATIVE EXAMPLE 1 Manufacture of Sheet-Like Top Pad

Toluene diisocyanate (TDI) as an isocyanate compound and polytetramethylene ether glycol (PTMEG) and diethylene glycol as polyol compounds were placed in a 4-neck flask. The reaction was allowed to proceed at 80° C. to prepare a prepolymer whose % NCO was 8-12 wt %.

The subsequent procedure was carried out in the same manner as in Example 1 to manufacture a sheet-like top pad.

TABLE 1 Amounts used during casting Comparative Example 1 Example 2 Example 1 Prepolymer (parts per weight) 100 100 100 Curing agent (parts per weight) 25 25 25 Surfactant (parts per weight) 0.2-1.5 0.2-1.5 0.2-1.5 Solid foaming agent (parts per 0.5-1.0 0.5-1.0 0.5-1.0 weight) Inert gas (L/min) 0.5-1.5 0.5-1.5 0.5-1.5

Manufacture of Polishing Pads

Each of the sheet-like top pads 10 was sequentially subjected to surface milling and grooving in accordance with general methods known in the art. The processed top pad was laminated on a sub-pad 30 to manufacture a polishing pad 100 having the structure illustrated in FIG. 1.

2. Evaluation of Physical Properties of the Polishing Pads

Strength and Contact Angle Evaluation

The polishing pads of Example 1, Example 2, and Comparative Example 1 were evaluated for physical properties, including contact angles for fumed silica slurry, CMP polishing performance, and the number of defects in wafers.

A groove-free central portion of each polishing pad was cut into a specimen having dimensions of 2 cm×2 cm. The contact angles of the specimen were measured using a dynamic contact angle analyzer (DCA-312, CAHN).

After the specimen was mounted in the analyzer, appropriate amounts of pure water (H₂O) and a fumed silica slurry filled in separate syringes were injected onto the specimen and the shapes of the droplets on the specimen were measured using the analyzer. The composition and preparation method of the fumed silica slurry are as follows.

Preparation of the Fumed Silica Slurry

First, a solution at pH 10.5 composed of a first pH adjusting agent (e.g., ammonia, potassium hydroxide or sodium hydroxide) and ultrapure water was prepared. ˜12 wt % of fumed silica (OCI) was added portion wise to the solution. The resulting mixture was dispersed using an ultrasonicator at a rate of 9000 rpm for about 4 h and was then further dispersed using a high-pressure homogenizer.

After sufficient dispersion, 0.5-2 wt % of an ammonium additive was added, followed by additional stirring for 1 h. Thereafter, 0.01-0.1 wt % of a nonionic surfactant was added and the pH of the resulting solution was adjusted to 10.5 using a second pH adjusting agent (e.g., ammonia, potassium hydroxide, sodium hydroxide, nitric acid or sulfonic acid).

The resulting solution was passed through slurry filters with 3.5 μm and 1 μm pore sizes (Micropore) to obtain the final fumed silica slurry. The physical properties of the final slurry were measured with a Zetasizer (nano-ZS 90, Malvern). As a result, the slurry was found to have a pH of 10.5 and an average particle size of 150 nm.

The physical properties of the sub-pads and the polishing pads as well as those of the top pads are shown in Table 2.

TABLE 2 Comparative Evaluation parameter Example 1 Example 2 Example 1 Physical Top pad Thickness (mm) 2 2 2 properties Hardness (Shore D) 59 59.5 59.8 Average pore size (μm) 28 27 28 Specific gravity (g/cc) 0.8 0.8 0.8 Tensile strength (N/mm²) 21.1 20.9 20.8 Elongation (%) 126 125 123 Shore D hardness values 58/54/51 58/54/51 58/54/51 at 30° C./50° C./70° C. Contact angle Ap (°, H₂O) 90 89 71 Contact angle Af (°, 88 86 70 Fumed silica slurry) * difference of the Contact angles 2.22% 3.37% 1.41% Sub-pad Type Non-woven Non-woven Non-woven fabric fabric fabric Thickness (mm) 1.1 1.1 1.1 Hardness (Asker C) 70 70 70 Polishing Thickness (mm) 3.32 3.32 3.32 pad Compression rate (%) 1.05 1.05 1.05 * The difference of Contact angles (Ad_((p−f)), %) was calculated by Ad_((p−f)) = [100*(Ap − Af)]/Ap where Ap is the contact angle for pure water and Af is the contact angle for the fumed silica slurry, which were measured at the same room temperature.

As can be seen from the results in Table 2, the hardness, average pore size, and specific gravity of the polishing pad of Comparative Example 1 were similar to those of the polishing pads of Examples 1 and 2 but the contact angles of the polishing pad of Comparative Example 1 for pure water and the fumed silica slurry were significantly different from those of the polishing pads of Examples 1 and 2.

Evaluation of Pore Physical Properties of the Top Pads

Each of the top pads was imaged by a scanning electron microscope (SEM) (JEOL) at a magnification of 100×. The number, size, and area proportion of the pores of the top pad were measured. The results are shown in FIG. 2 and Table 3.

TABLE 3 Pore physical properties Comparative of the top pads Example 1 Example 2 Example 1 Number average diameter (μm) 28.3 26.8 28 Counts/0.3 cm² (ea) 412 405 402 Area proportion (%) 40.1 40 39.8

Evaluation of Polishing Properties

The removal rates and cut rates (μm/hr) of the polishing pads of Example 1, Example 2, and Comparative Example 1 and the number of defects in wafers after polishing with the polishing pads were measured by the following procedures.

1) Removal Rate Measurement

A 300 mm-diameter silicon wafer deposited with silicon oxide by CVD was mounted in a CMP polisher. The silicon wafer was set on a platen attached with the porous polyurethane polishing pad such that the silicon oxide layer of the silicon wafer faced the underlying polishing pad. Thereafter, the polishing load was adjusted to 4.0 psi. A calcined ceria slurry was supplied at a rate of 250 ml/min on the polishing pad while rotating the platen at 150 rpm for 60 sec to polish the silicon oxide layer. After polishing, the silicon wafer was detached from the carrier, mounted in a spin dryer, washed with deionized water (DIW), and dried with nitrogen for 15 sec. The thickness of the dried silicon wafer was measured and compared with that of the silicon wafer before polishing. The thicknesses of the silicon wafer before and after polishing were measured using a spectral interference thickness meter (SI-F80R, Kyence).

The removal rate was calculated by Equation 2:

Removal rate=Thickness of silicon wafer after polishing (Å)/Polishing time (60 sec)   [Equation 2]

2) Cutting Rate Measurement

Each of the polishing pads was pre-conditioned with deionized water for the first 10 min and was then conditioned by spraying deionized water for 1 h. The thickness variation was measured during the 1-h conditioning.

A conditioning system (AP-300HM, CTS) was used for conditioning. The conditioning pressure and the rotational speed were adjusted to 6 lbf and 100-110 rpm, respectively. A disk pad (LPX-DS2, SAESOL) was used for conditioning.

3) Defect Measurement

Polishing was performed using a CMP polisher in the same manner as described in the removal rate measurement.

After polishing, the silicon wafer was transferred to a cleaner and cleaned sequentially with 1 wt % HF, deionized water (DIW), 1 wt % H₂NO₃, and deionized water (DIW) (for 10 sec each). Thereafter, the cleaned silicon wafer was transferred to a spin dryer, washed with deionized water (DIW), and dried with nitrogen for 15 sec.

The number of defects in the dried silicon wafer was measured and compared with that in the silicon wafer before polishing. The numbers of defects before and after polishing were measured using a defect inspection system (XP+, Tencor).

The removal rates (RR), the cutting rates, and the numbers of defects (# defects per about 300 mm diameter disc, about 70685.83 mm²) are shown in Table 4, FIG. 3 and FIG. 4.

TABLE 4 Comparative Example 1 Example 2 Example 1 RR (Å/min) 2733 2754 2759 Number of defects 7 5 50 Cutting rate (μm/hr) 51 53 50 *Rate of reduction (%) in the 86% 90% — number of defects compared to Comparative Example 1 *Rate of reduction (%) in the number of defects was calculated by [(the number of defects after polishing with the polishing pad of Comparative Example 1) − (the number of defects after polishing with the polishing pad of Example 1)*100]/(the number of defects after polishing with the polishing pad of Comparative Example 1).

As can be seen from the results in Table 4, the removal rates and cutting rates of the polishing pads of Examples 1 and 2 were similar to those of the polishing pad of Comparative Example 1, but the numbers of defects in the wafers after polishing with the polishing pads of Examples 1 and 2 were significantly reduced compared to that after polishing with the polishing pad of Comparative Example 1.

The use of the polishing pad according to the examples described herein leads to a significant reduction in the number of defects while maintaining a removal rate and cutting rate at levels equal to those of conventional polishing pads. In addition, the method of the examples described herein is suitable for manufacturing the polishing pad. Furthermore, the polishing method of the examples described herein is suitable for polishing wafers.

While specific examples have been shown and described above, it will be apparent after an understanding of this disclosure that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. Therefore, the scope of this disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in this disclosure. 

What is claimed is:
 1. A polishing pad comprising a polyurethane, wherein the polyurethane comprises in its main chain a silane repeating unit represented by Formula 1, wherein the number of defects on a substrate after polishing with the polishing pad and a fumed silica slurry is 40 or less;

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to
 30. 2. The polishing pad according to claim 1, wherein the polyurethane comprises in its main chain a repeating unit represented by Formula 2-1 or 2-2:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and R₂₁ is —Si(R₁₃)(R₁₄)(R₂₂)—, wherein R₁₃ and R₁₄ are each independently hydrogen or a C₁-C₁₀ alkyl group, and R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), and n is an integer from 1 to
 30. 3. The polishing pad according to claim 1, wherein the difference of a contact angle of the polishing pad for pure water and a contact angle of the polishing pad for a fumed silica slurry is 1.5 to 5, as calculated by Equation 1: Ad _((p−f))(%)=[100×(Ap−Af)]/Ap   [Equation 1] where Ap is the contact angle for pure water, Af is the contact angle for a fumed silica slurry, and Ad_((p−f)) is the difference of the contact angles.
 4. The polishing pad according to claim 1, wherein the polyurethane is in the form of a foamed body with an average pore size of 10 to 30 μm.
 5. The polishing pad according to claim 1, wherein the polyurethane has a Shore D hardness of 55 to
 65. 6. The polishing pad according to claim 1, further comprising a top pad comprising the polyurethane and a sub-pad disposed on the top pad, wherein the sub-pad is a non-woven fabric or suede type.
 7. A polishing pad comprising a top pad as a polyurethane polishing layer, wherein the polyurethane polishing layer comprises a foamed body of a urethane composition, wherein the urethane composition comprises a urethane prepolymer, a curing agent, and a foaming agent, wherein the urethane prepolymer is a copolymer of a prepolymer composition comprising an isocyanate compound, an alcohol compound, and a silane compound, wherein the silane compound comprises a silane repeating unit and comprises at least one end terminated with a hydroxyl, amine or epoxy group, and the silane repeating unit is represented by Formula 1:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to
 30. 8. The polishing pad according to claim 7, wherein the prepolymer composition comprises the silane compound in an amount of 0.1 to 5% by weight, based on the total weight of the prepolymer composition.
 9. The polishing pad according to claim 7, wherein the top pad reduces a number of defects of a silicon wafer after polishing by 80% or more compared to polyurethane foamed body without the silane repeating unit represented by Formula
 1. 10. The polishing pad according to claim 7, wherein the silane compound is represented by Formula 3:

wherein R₁₁, R₁₂, R₁₃, and R₁₄ are each independently hydrogen or C₁-C₁₀ alkyl groups, R₂₂ is —(CH₂)_(m1)— or —(CH₂)_(m2)—(OCH₂CH₂)_(m3)— (wherein m1, m2, and m3 are each independently an integer from 1 to 20), R₃₁ is C₁-C₂₀ alkylene groups, R₄₁ and R₄₂ are each independently a hydroxyl, amine or epoxy group, and n is an integer from 1 to
 30. 11. The polishing pad according to claim 7, wherein the % NCO of the prepolymer is from 8 to 12% by weight.
 12. A method for manufacturing a polishing pad, comprising i) preparing a polyurethane in the form of a foamed body with polymerizing a urethane composition, ii) manufacturing a top pad comprising the polyurethane, and iii) fixing the top pad to a sub-pad by lamination to prepare the polishing pad, wherein the urethane composition comprises a urethane prepolymer, a curing agent, and a foaming agent, and wherein the foamed body comprises a repeating unit represented by Formula 1, and the main chain of the polyurethane contains the silane repeating unit:

wherein R₁₁ and R₁₂ are each independently hydrogen or C₁-C₁₀ alkyl groups, and n is an integer from 1 to
 30. 13. The method according to claim 12, wherein the urethane prepolymer is prepared by a method comprising allowing a prepolymer composition to react at 50 to 120° C., and the % NCO of the urethane prepolymer is from 8 to 12% by weight, wherein the prepolymer composition comprises an isocyanate compound, an alcohol compound, and a silane compound, wherein the silane compound comprises the silane repeating unit of Formula 1 and at least one end group with a hydroxyl, amine or epoxy group.
 14. The method according to claim 13, wherein the preparation of the urethane prepolymer comprises: mixing the isocyanate compound and the alcohol compound to prepare a first composition and allowing the first composition to react at 60 to 100° C. for 1 to 5 hours to prepare a first polymer (first step); and mixing the first polymer and the silane compound to prepare a second composition and allowing the second composition to react at 60 to 100° C. for 0.5 to 3 hours to prepare a second polymer (second step).
 15. A method for producing a polished wafer, comprising mounting the polishing pad according to claim 1 and an unpolished wafer in a chemical mechanical planarization (CMP) polisher and polishing the unpolished wafer with the polishing pad while feeding a polishing slurry into the CMP polisher. 